STEREO's launch has been postponed to no earlier than Sept. 18, the opening of the mission's next launch window. The additional time is necessary for further evaluation of the Delta II second stage to verify it is structurally sound for flight. This concern arose after further engineering analysis revealed that a similar tank produced for another mission was marginally thin in an area of the oxidizer tank. Engineers are assessing several options for the STEREO launch vehicle at Pad 17-B to determine the thickness of the tank in this same area.

STEREO was not transported from Astrotech to the launch pad over the weekend as planned. It will remain at the payload processing facility until the necessary course of action for the Delta II can be more clearly defined.